1. Field of the Invention
The present invention relates to a fuel pump control device, and more particularly to a fuel pump control device allowing a fuel pump having a small capacity to feed a sufficient amount of fuel to an internal combustion engine.
2. Description of Background Art
As described in Japanese Utility Model Publication Nos. Hei 2-31566 and Hei 6-14069, control devices for controlling an electrically-operated fuel pump for feeding fuel to an internal combustion engine have been configured such that a relay means is connected between the fuel pump and a battery, wherein the fuel pump is intermittently operated by opening/closing the relay means on the basis of an ignition signal for an engine.
FIG. 4 is a block diagram showing an essential portion of the above-described related art fuel pump control device. Referring to FIG. 4, a fuel pump control device 3 includes a thyristor (SCR) 301 as a relay means and an ignition circuit 302. The thyristor 301 is connected, together with an ignition switch 2, in series between a fuel pump 6 and a battery 1. An ignition coil 5 and an ignitor 4 connected in series to each other are connected in parallel to the battery 1 via the ignition switch 2. An ignition pulse is supplied from the ignition coil 5 to the ignition circuit 302. Accordingly, the thyristor 301 is opened/closed one time for each ignition of the engine, to thereby intermittently drive the fuel pump.
The thyristor 301 as the relay means, which has no mechanical contact, is excellent in durability; however, it has a large voltage drop ΔV at a PN junction. As a result, a drive voltage applied to the fuel pump 6 is lower than a battery voltage by the voltage drop ΔV. On the other hand, as shown in FIG. 5, since the feeding ability of the fuel pump is, generally, largely dependent on a drive voltage. Accordingly, if the drive voltage is reduced as described above, the fuel pump cannot feed a sufficient amount of fuel. For this reason, in the case of adopting the thyristor as the relay means, there occurs a problem that it is required to use a fuel pump having a large capacity, that is, a large-sized, expensive fuel pump for feeding a sufficient amount of fuel even if the drive voltage applied to the fuel pump is lower than the battery voltage.